Oxidation of alkylaromatics

ABSTRACT

A process for the controlled oxidation of alkyaromatic compounds comprises reacting said compounds with an oxidising system, comprising cobalt (II) ions, bromide ions, and hydrogen peroxide, in the presence of an appropriate protic solvent. 
     The process is particularly useful in the selective oxidation of poly(alkyl)aromatic compounds.

This Application is a 371 of PCT/GB92/01076 filed 16 Jun. 1992.

This invention concerns a process for the oxidation of alkylaromaticcompounds using an oxidising system comprising cobalt salts and hydrogenperoxide.

The oxidation of alkylaromatic compounds using oxidising systemscomprising cobalt salts is known in the art.

U.S. Pat. Nos. 3,665,030 and 3,969,405 disclose that alkylaromaticcompounds may be oxidised to aromatic carboxylic acids using anoxidation system comprising a cobalt acetate catalyst, acid activatorand molecular oxygen oxidant. The reaction is not commerciallysatisfactory for the preparation of carboxylic acids since the reactiontimes required to obtain high conversion rates are too long.Furthermore, the reaction tends not to be selective in the preparationof monocarboxylic acid aromatics from poly(alkyl)aromatics (see U.S.Pat. No. 3,665,030, particularly Example XXVI and Example XXXVII, andU.S. Pat. No. 3,969,405, particularly Examples XXXVII to XLIV).

U.S. Pat. Nos. 4,323,692 and 4,401,828 disclose that phenoxytoluenes maybe oxidised to phenoxybenzoic acids in the presence of from 0.001 to 0.5moles of a cobalt (II) salt catalyst per mole of phenoxytoluene, from 1to 3 equivalents of bromide ion per mole of cobalt (II) salt, from 0.5to 1 mole of hydrogen peroxide activator per mole of cobalt (II) saltand the introduction of gaseous oxygen oxidant.

U.S. Pat. No. 3,519,684 discloses a process for producing aromaticdicarboxylic acids from di(alkyl)aromatic compounds using an oxidisingsystem comprising a cobalt salt catalyst, peracetic acid activator andthe introduction of gaseous oxygen oxidant.

It is an object of the present invention to provide a process for theoxidation of alkylaromatic compounds, which process does not essentiallyrequire the introduction of gaseous oxygen.

It is a further object of the present invention to provide a process forthe oxidation of alkylaromatic compounds which process may achieve highconversion and high yields of oxidised products by a one-pot reaction.

It is yet a further object of the present invention to provide a processfor the selective oxidation of poly(alkyl)aromatic compounds to formaromatic carboxylic acid compounds, which process does not essentiallyrequire the introduction of gaseous oxygen as oxidant.

In accordance with the present invention, there is provided a processfor oxidising an alkylaromatic compound, which process comprisesreacting said alkylaromatic compound with an oxidising system comprisingfrom at least 0.01 moles of cobalt (III) ions per mole of alkylaromaticcompound, from at least 0.01 moles of bromide ions per mole ofalkylaromatic compound, and from more than 0.5 mole, preferably morethan 1 mole, of hydrogen peroxide per mole of alkylaromatic compound, inthe presence of an appropriate protic solvent selected from the groupconsisting of the carboxylic acids having from one to five carbon atoms,said alkylaromatic compound having at least one alkyl substituent whichis not tertiary at the carbon positioned alpha to the aromatic ring.

The preferred protic solvents are acetic acid, propionic acid andbutyric acid, the most preferred being acetic acid. The protic solventmay be present in any reasonable amount but is preferably present in anamount of at least 3 times the weight of the alkylaromatic compound andpreferably no more than 15 times, such as from 3 to 12 times, the weightof the alkylaromatic compound. When the alkylaromatic compound is apoly(alkyl) aromatic compound, the preferred amount of protic solventused is from 4 to 10 times the weight of the poly(alkyl)aromaticcompound. When the alkylaromatic compound is a mono-alkylaromaticcompound, the preferred amount of protic solvent used is from 8 to 12times the weight of the mono-alkylaromatic compound.

In the process of the present invention, the cobalt (III) ions arepreferably sourced from an in-situ oxidation of cobalt (II) ions. Thecobalt (II) ions may be sourced from any appropriate cobalt (II) salt,such as cobalt (II) acetate, cobalt (II) propionate, cobalt (II)naphthenate and cobalt (II) bromide. Cobalt (II) acetate is preferred.

The cobalt (III) ions are preferably present in the oxidising system inan amount of from about 0.01 to about 0.15 moles cobalt (III) ions permole of alkylaromatic compound. Preferably, when the alkyaromaticcompound is a poly(alkyl)aromatic compound, the amount of cobalt (III)ions required is about 0.03 to about 0.1 moles of cobalt (III) ions permole of poly(alkyl)aromatic compound. Preferably, when the alkylaromaticcompound is a mono-alkylaromatic compound, the amount of cobalt (III)ions required is from about 0.02 to about 0.12 moles, more preferablyfrom about 0.06 to about 0.12 moles, per mole of mono-alkylaromaticcompound

The bromide ions (Br⁻), which are preferably present in the oxidisingsystem in an amount of from about 0.01 to about 0.20 moles Br⁻ per moleof alkylaromatic compound, are preferably sourced from bromine, hydrogenbromide or any appropriate bromide salt, such as ammonium bromide,cobalt (II) bromide, sodium bromide or potassium bromide. Sodium bromideis preferred. When the alkylaromatic compound is a poly(alkyl)aromaticcompound, the preferred bromide ion content is from about 0.04 to 0.2moles, more preferably 0.04 to 0.15 moles, per mole of poly(alkyl)aromatic compound, whereas the preferred amount of bromide ions presentwhen the alkylaromatic compound is a mono-alkylaromatic compound is fromabout 0.02 to 0.2 moles, more preferably 0.06 to 0.2 moles, yet morepreferably 0.06 to 0.16 moles, per mole of mono-alkylaromatic compound.

Hydrogen peroxide is present in the present invention in an amount ofmore than 0.5 mole hydrogen peroxide per mole of alkylaromatic compound.Preferably, from about 1 to about 10 moles, more preferably from about 2to about 10 moles, of hydrogen peroxide are present per mole ofalkylaromatic compound to be oxidised. Even more preferably from about 3to about 10 moles and most preferably from about 4 to about 8 moles ofhydrogen peroxide are used per mole of alkylaromatic compound.

The hydrogen peroxide is preferably added as an aqueous solution, whichsolution desirably has a strength of at least 25% peroxide. Preferablythe solution is not stronger than 85% peroxide. The preferred solutionhas a strength of from about 35% to about 70% peroxide.

The alkylaromatic compounds which are oxidised most satisfactorily bythe process of the present invention are those which comprise at leastone alkyl, preferably a (C₁ -C₆)alkyl, substituent having at least onehydrogen atom at the alpha position relative to the aromatic ring.Although higher alkyl substituents may be oxidised by the process of thepresent invention, such as those having up to 30 carbon atoms, (C₁-C₆)alkyl substituents are preferred. From the preferred group ofsubstituents, straight chain (C₁ -C₆)alkyl substituents and branchedchain alkyl substituents having less than 5 carbons are most preferred.Typical alkylaromatic compounds which may be oxidised by the presentinvention include mono-, di- or tri-alkylbenzenes, such as toluene,ethylbenzene, p-t-butyltoluene, cumene, o-, m- or p-xylenes, o-, m-,p-diethylbenzenes, tri-methylbenzenes, e.g. mesitylene, and polynuclearalkylaromatic compounds such as the mono-, di- and tri-alkylnaphthalenes, e.g. methyl naphthalenes, ethyl naphthalenes anddimethylnaphthalenes.

The alkyl substituent or substituents of the alkylaromatic compounds maybe any substituted alkyl which may be oxidised to an alcohol, a ketoneor carboxylic acid as may be appropriate. Such substituted alkylscommonly have at least one hydrogen atom or hydroxy group at the alphaposition relative to the aromatic ring. Alkyls substituted with at leastone phenyl-, hydroxy-, halo- or oxy- substituent are typical of thesubstituted-alkylaromatic compounds which may be oxidised by the processof the present invention. For example, when the alkyl- substituent ismethyl-, the methyl- may be a mono- or di-substituted methyl- of theformulae CHR¹ R² -- or C(OH)R¹ R² -- where R¹ and R² are independentlyselected from the group consisting of H-, substituted or unsubstitutedphenyl-, --OH and hal- (halis F-, Ci-, Br- or I-), or R¹ and R² togetherare ═O (oxy) i.e. an aidehyde. Typical substituted-alkylaromaticcompounds are diphenylmethane and diphenylethane.

For the avoidance of doubt, reference herein to the alkyl substituentnot being tertiary at the carbon positioned alpha to the aromatic ringindicates that the substituent is a methyl group, or is primary orsecondary at the alpha carbon, although the alkyl substituent maycontain a tertiary alkyl group elsewhere.

The alkylaromatic compounds may also be substituted on the aromatic byone or more substituents such as fluoro, chloro, bromo, iodo, nitro, oroxygenated substituents such as acyl, alkoxy, carboxyl, phenoxy and1-acyloxyalkyl. Typical of such substituted alkylaromatic compounds arep-chlorotoluene, p-bromomethylbenzene, m-nitrotoluene, o-acetyltoluene,4-methoxyethylbenzene, p-toluic acid, 4-methyl-1-naphthoic acid,3-(2-chloro-4-trifluoromethylphenoxy)toluene,4,4'-dichlorodiphenylmethane and 2,4-dichloro-diphenylmethane.

The process of the present invention is preferably effected at aboutatmospheric pressure, at a preferred temperature of at least 40° C.Preferably, the process is effected at a temperature of at least 60° C.The maximum temperature of the process at atmospheric pressure isdetermined by the reflux temperature of the mixture, which is usuallyabout 100° C.

The overall reaction time of the process is unlikely to be less than 15minutes and is typically run for between about 1 and 5 hours, whilelonger than 8 hours is very unusual. The reaction times of the processesof the present invention will typically be substantially less than thetimes accorded to the cobalt catalysed processes exemplified in U.S.Pat. Nos. 3,969,405 and 3,665,030, thereby demonstrating the commercialadvantage of the present invention.

The cobalt and bromide catalyst for the reaction may be recovered oncompletion of the desired reaction, and may be recycled, so as toimprove the costs and reduce the environmental impact of the process.

It has been surprisingly found that the process of the present inventiongives preferential oxidation of poly(alkyl)aromatic compounds. Forexample, it has been found that the controlled oxidation process whenapplied to a poly(alkyl)aromatic compound will selectively oxidise onlyone alkyl group through to the carboxylic acid before a second alkylgroup is attacked to any significant degree. This is an extremelyadvantageous aspect of the present invention since the known processesof U.S. Pat. No. 3,969,405 do not demonstrate such selectivity.

The process of the present invention may be performed to producealcohols, aldehydes, ketones or acids of the alkylaromatics, and istherefore very flexible. In some instances, for the production ofaldehydes for example, it may be necessary for the process to be carriedout under an inert atmosphere, such as nitrogen or argon, to prevent thereaction completing oxidation to the acid, though in other instances itmay be found that the reaction stops at the aldehyde stage withoutrapidly progressing to the completely oxidised acid stage. On the otherhand, where a mixture of aldehyde and acid is formed, it would bepossible to force the reaction to complete oxidation by the use of asecond oxidant, such as air, peracetic acid or sodium perborate.

The process according to the present invention may also be operatedunder forcing conditions so that the oxidation proceeds with reducedselectivity if the products of such a non-selective process areparticularly desired. This may be the case where the substrate is apoly(alkyl) aromatic and it is desired to oxidise a plurality of thealkyl substituents in one reaction. Typically, such forcing conditionswould comprise a combination of a temperature in the range of from about80° C. to about 100° C., use of a hydrogen peroxide solution comprisinggreater than about 65% H₂ O₂ by weight.

The invention will now be further described with reference to thefollowing examples:

EXAMPLE I

This example demonstrates the oxidation of toluene by the process of thepresent invention.

Cobalt (II) acetate tetrahydrate (lg, 0.004 moles), sodium bromide (lg,0.01 moles), toluene (0.054 moles) and acetic acid (55 g) were chargedto a vessel fitted with an overhead paddle stirrer, thermometer andcondenser and heated to 80° C. Hydrogen peroxide (40%, 0.44 moles) wasadded dropwise down the condenser over 2 hours, during which time thereaction mixture changed colour from dark blue to pink. The reaction wascontinued for a further two hours when it was stopped and the reactionmixture analysed by HPLC. The analysis revealed that 90.6% of thetoluene had been consumed, yielding products including benzaldehyde(29.0% yield) and benzoic acid (55.6% yield).

EXAMPLE II

This is a comparative example demonstrating the oxidation of toluene bythe prior art process described in U.S. Pat. No. 3,969,405.

The procedure of Example I was repeated, but this time no hydrogenperoxide was used. Instead, the reaction mixture was stirred vigorously,thereby ensuring full exposure of the reaction mixture to molecularoxygen (air), over the complete four hour period. The final reactionmixture was analysed by HPLC and it was revealed that 37.6% of thetoluene had been consumed, yielding products including benzaldehyde(2.37% yield) and benzoic acid (4.33% yield).

A comparison of the results from Example I with the results from ExampleII clearly demonstrates the superior performance of the oxidationprocess of the present invention.

EXAMPLE III

The procedure of Example I was repeated, but this time cobalt (II)acetate tetrahydrate (0.003 moles), sodium bromide (0.005 moles),ethylbenzene (0.027 moles) and hydrogen peroxide (35%, 0.22 moles) wereused. The final reaction mixture, analysed by HPLC, revealed that 97.0%of the ethylbenzene had been consumed, yielding products includingacetophenone (91.1% yield).

EXAMPLE IV

The procedure of Example III was repeated, but this time cumene (0.056moles) and hydrogen peroxide (35%, 0.22 moles) were used. The reactionmixture, analysed by HPLC, revealed that 87.4% of the cumene had beenconsumed, yielding products including acetophenone (43.1% yield) and2-phenyl-2-propanol (30.6% yield).

EXAMPLE V

The procedure of Example I was repeated, but this time cobalt (II)acetate tetrahydrate (0.008 moles), sodium bromide (0.04 moles),diphenylmethane (0.055 moles) and hydrogen peroxide (35%, 0.28 moles)were used. The final reaction mixture, analysed by HPLC, revealed that91.5% of the diphenylmethane had been consumed, yielding productsincluding benzophenone (72.3% yield).

EXAMPLE VI

The procedure of Example I was repeated, but this time cobalt (II)acetate tetrahydrate (0.012 moles), sodium bromide (0.05 moles),dichlorotoluene (0.074 moles), acetic acid (100 g) and hydrogen peroxide(70%, 0.68 moles) were used and the reaction was performed at 90° C. forthree hours. The final reaction mixture, analysed by HPLC, revealed that66.0% of the dichlorotoluene had been consumed, yielding productsincluding dichlorobenzaldehyde (15.2% yield) and dichlorobenzoic acid(23.8% yield).

EXAMPLE VII

This example demonstrates the oxidation of dichlorotoluene by the priorart process described in U.S. Pat. No. 3,969,405.

The procedure of Example VI was repeated, but this time no hydrogenperoxide was used. Instead, molecular oxygen (air) was bubbled throughthe reaction mixture for sixteen hours. The final reaction mixture,analysed by HPLC, revealed that none of the dichlorotoluene hadundergone oxidation.

A comparison of the results from Example VI with the results fromExample VII demonstrates the superior performance of the process of thepresent invention over the process of the prior art.

EXAMPLE VIII

The procedure of Example I was repeated, but this time cobalt (II)acetate tetrahydrate (0.008 moles), sodium bromide (0.001 moles),toluene (0.056 moles) and hydrogen peroxide (35%, 0.21 moles) were usedand the reaction carried out at 44° C. for three hours in total under anitrogen atmosphere. The final reaction mixture, analysed by HPLC,revealed that 46.8% of the toluene had been consumed, yielding productsincluding benzaldehyde (29.7% yield). No benzoic acid was detected,illustrating that the process can be controlled to give oxidation toaldehydes in preference to acids.

EXAMPLE IX

The procedure of Example I was repeated, but this time cobalt (II)bromide (0.005 moles) (instead of cobalt (II) acetate tetrahydrate andsodium bromide) and hydrogen peroxide (40%, 0.22 moles) and the reactionwas performed at 60° C. for a total of 3.5 hours. The final reactionmixture, analysed by HPLC, revealed that 70.2% of the toluene had beenconsumed, yielding products including benzaldehyde (27.2% yield) andbenzoic acid (41.7% yield). This example demonstrates the suitability ofcobalt (II) bromide as a source of cobalt (II) ions and bromide ions.

EXAMPLE X

The procedure of Example I was repeated, but this time Cobalt (II)acetate tetrahydrate (0.5 g, 0,002 moles), bromine (0.5 g, 0,003 moles),toluene (2.58 g, 0.028 moles), acetic acid (25 g) and hydrogen peroxide(35%, 0.22 moles) were used. The total reaction time was 3 hours. Theanalysis of the reaction mixture revealed that 79.2% of the toluene hadbeen consumed, yielding products including benzylalcohol (6.6% yield),benzaldehyde (31.54% yield) and benzoic acid (25.18% yield).

EXAMPLE XI

This example demonstrates the selective oxidation of p-xylene by theprocess of the present invention.

Cobalt (II) acetate tetrahydrate (0.5 g, 0,002 moles), sodium bromide(0.005 moles), p-xylene (0.027 moles) and 25 g acetic acid were chargedto a vessel fitted with a condenser, overhead paddle stirrer andthermometer and heated to 80° C. Hydrogen peroxide (40%, 0.22 moles) wasadded dropwise over 40 minutes down the condenser. During this time thereaction mixture changes from a deep blue colour to pink. The reactionwas continued for a further 80 minutes when the reaction was stopped andthe reaction mixture analysed by HPLC. The analysis revealed that 84.8%of the toluene had been consumed, yielding products includingtolualdehyde (44.9% yield) and toluic acid (12.6% yield). The reactionmixture contained substantially no polyoxidised products such asterephthalic acid.

EXAMPLE XII

This example illustrates the selective oxidation of mesitylene by theprocess of the present invention.

Cobalt (II) acetate tetrahydrate (0.5 g, 0.002 moles), sodium bromide(1.5 g, 0.015 moles), mesitylene (0.083 moles) and acetic acid (40 g)were charged to a vessel fitted with a condenser, overhead paddlestirrer and thermometer and heated to 80° C. Hydrogen peroxide (50%,11.5g 100% equivalent; 0.34 moles) was added dropwise over a period of40 minutes down the condenser. During this period, it was noted that thereaction mixture changed from a deep blue colour to pink. The reactionwas continued for a further 80 minutes when it was stopped and thereaction mixture analysed by GC. The analysis showed that 92.4% of themesitylene had been converted to oxidised products. The oxidisedproducts included 3,5-dimethyl benzaldehyde (31.4% yield) and3,5-dimethyl benzoic acid (35.4% yield). Substantially no polyoxidisedproducts were found in the reaction mixture.

EXAMPLE XIII

Cobalt (II) acetate tetrahydrate (0.5 g, 0.002 moles), sodium bromide(0.5 g, 0.005 moles), benzyl alcohol (2.93 g, 0.027 moles) and aceticacid (25 g) were charged to a vessel fitted with a overhead paddlestirrer, thermometer and condenser and heated to 80° C. Hydrogenperoxide (30%, 0.22 moles) was added dropwise down the condenser overtwo hours during which time the reaction mixture changed colour fromdeep blue to pink. The reaction was continued for a further 90 minutesafter which it was stopped and analysed by HPLC. The analysis revealedthat 99.0% of the benzyl alcohol had been consumed, yielding productsincluding benzaldehyde (50.2% yield) and benzoic acid (48.8% yield).

EXAMPLE XIV

The procedure of Example XIV was repeated, but this time benzaldehyde(2.88 g, 0.027 moles) was used. The reaction mixture, analysed by HPLC,showed that 84.7% of the benzaldehyde had been consumed, yieldingproducts including benzoic acid (81.7% yield).

EXAMPLE XV

This example illustrates the use of forcing conditions which achieveless selective poly oxidation.

Cobalt (II) acetate tetrahydrate (0.6g, 0.0024 moles), sodium bromide(1.7g, 0.017 moles), 1,2,3-trimethylbenzene (10 g, 0.083 moles) andacetic acid (47 g) were charged to a vessel fitted with a condenser,overhead paddle stirrer and thermometer and heated to 100° C. Hydrogenperoxide (70%, 16.1 g 100% equivalent; 0.47 moles) was added dropwiseover a period of 80 minutes down the condenser. The reaction wascontinued for a further 80 minutes when it was stopped and the reactionmixture analysed by GC. The analysis showed that the products comprisedmethyl-2,3-benzenedicarboxaldehyde, methyl-2,6-benzenedicarboxaldehyde,2,3-dimethylbenzoic acid and 2,6-dimethylbenzoic acid. As estimated fromGC peak areas, the two acids comprised approximately 70% of the product,the two aldehydes comprising approximately 30% of the product.

We claim:
 1. A process for oxidising an alkylaromatic compoundcomprising reacting said alkylaromatic compound with an oxidising systemin the presence of a protic solvent selected from the group consistingof carboxylic acids having one to five carbon atoms, said alkylaromaticcompound having at least one alkyl substituent which is not tertiary atthe carbon positioned alpha to the aromatic ring, said oxidising systemcomprising at least 0.01 moles of cobalt (III) ions per mole ofalkylaromatic compound, at least 0.01 moles of bromide ions per mole ofalkylaromatic compound, and more than 0.5 mole of hydrogen peroxide permole of alkylaromatic compound.
 2. A process as claimed in claim 1,wherein an alkyl substituent of the alkylaromatic compound has at leastone hydrogen atom at the alpha position relative to the aromatic ring.3. A process as claimed in claim 1 or claim 2, wherein the alkylaromaticcompound comprises a poly(alkyl)aromatic compound.
 4. A process asclaimed in claim 3, wherein said alkylaromatic compound has a pluralityof identical alkyl substituents.
 5. A process as claimed in claim 3,wherein the cobalt (III) ions are present in an amount of from 0.03 to0.1 moles per mole of poly(alkyl)aromatic compound.
 6. A process asclaimed in claim 3, wherein the bromide ions are present in an amount offrom 0.04 to 0.15 moles per mole of poly(alkyl)aromatic compound.
 7. Aprocess as claimed in claim 3, wherein the protic solvent is present inan amount of 3 to 12 times the weight of the poly(alkyl)aromaticcompound.
 8. A process as claimed in claim 3, wherein the cobalt (III)ions are present in an amount of from 0.03 to 0.1 moles per mole ofpoly(alkyl)aromatic compound, and the bromide ions are present in anamount of from 0.04 to 0.15 moles per mole of poly(alkyl)aromaticcompound.
 9. A process as claimed in claim 8, wherein the protic solventis present in an amount of 4 to 10 times the weight of thepoly(alkyl)aromatic compound.
 10. A process as claimed in claim 3,wherein the hydrogen peroxide is present in an amount of from 4 to 8moles per mole of poly(alkyl)aromatic compound.
 11. A process as claimedin claim 1 or claim 2, wherein the alkylaromatic compound comprises amonoalkylaromatic compound.
 12. A process as claimed in claim 11,wherein the cobalt (III) ions are present in an amount of from 0.02 to0.12 moles per mole of monoalkylaromatic compound.
 13. A process asclaimed in claim 12, wherein the cobalt (III) ions are present in anamount of from 0.06 to 0.12 moles per mole of monoalkylaromaticcompound.
 14. A process as claimed in claim 11, wherein the bromide ionsare present in an amount of from 0.02 to 0.2 moles per mole ofmonoalkylaromatic compound.
 15. A process as claimed in claim 14,wherein the bromide ions are present in an amount of from 0.06 to 0.16moles per mole of monoalkylaromatic compound.
 16. A process as claimedin claim 11, wherein the protic solvent is present in an amount of from3 to 15 times the weight of monoalkylaromatic compound.
 17. A process asclaimed in claim 11, wherein the cobalt (III) ions are present in anamount of from 0.02 to 0.12 moles per mole of monoalkylaromatic compoundand the bromide ions are present in an amount of from 0.02 to 0.2 molesper mole of monoalkylaromatic compound.
 18. A process for oxidising amonoalkylaromatic compound comprising reacting said monoalkylaromaticcompound with an oxidising system in the presence of a protic solventselected from the group consisting of carboxylic acids having from oneto five carbon atoms, said monoalkylaromatic compound having an alkylsubstituent which is not tertiary at the carbon positioned alpha to thearomatic ring, said oxidising system comprising 0.02 to 0.12 moles ofcobalt (III) ions per mole of monoalkylaromatic compound, 0.02 to 0.2moles of bromide ions per mole of monoalkylaromatic compound and morethan 0.5 mole of hydrogen peroxide per mole of monoalkylaromaticcompound.
 19. A process as claimed in claim 18, wherein the cobalt (III)ions are present in an amount of from 0.06 to 0.12 moles per mole ofmonoalkylaromatic compound.
 20. A process as claimed in claim 18,wherein the bromide ions are present in an amount of from 0.06 to 0.12moles per mole of monoalkylaromatic compound.
 21. A process as claimedin claim 18, wherein the protic solvent is present in an amount of from8 to 12 times the weight of monoalkylaromatic compound.
 22. A process asclaimed in claim 11, wherein the hydrogen peroxide is present in anamount of from 3 to 10 moles per mole of monoalkylaromatic compound. 23.A process as claimed in claim 22, wherein the hydrogen peroxide ispresent in an amount of from 4 to 8 moles per mole of monoalkylaromaticcompound.
 24. A process as claimed in any one of claims 1, 2, or 18-21,wherein an alkyl substituent of the alkylaromatic compound is a (C₁ -C₆)alkyl substituent.
 25. A process as claimed in claim 24, wherein analkyl substituent of the alkylaromatic compound is a methyl substituent.26. A process as claimed in any one of claims 1, 2, or 18-21, wherein analkyl substituent of the alkylaromatic compound is substituted with atleast one phenyl-, hydroxy-, halo or oxy-substituent.
 27. A process asclaimed in claim 24, wherein the aromatic substituent of thealkylaromatic compound is substituted with at least one fluoro, chloro,bromo, iodo, nitro or oxygenated substituent.
 28. A process as claimedin any one of claims 1, 2, or 18-21, wherein the cobalt (III) ions areformed in-situ by the oxidation of cobalt (II) ions sourced from acobalt (II) salt selected from the group consisting of cobalt (II)acetate, cobalt (II) propionate, cobalt (II) naphthenate and cobalt (II)bromide.
 29. A process as claimed in any one of claims 1, 2, or 18-21,wherein the bromide ions are sourced from bromide or a bromide saltselected from the group consisting of hydrogen bromide, ammoniumbromide, cobalt (II) bromide, sodium bromide and potassium bromide. 30.A process as claimed in any one of claims 1, 2, or 18-21, wherein theprocess is effected at a temperature of at least 40° C.
 31. A process asclaimed in claim 8, wherein the process is effected at a temperature ofat least 60° C.
 32. A process as claimed in any one of claims 1, 2, or18-21, wherein the process employs forcing conditions comprising acombination of a temperature in the range of from 80° C. to 100° C. andto use of a hydrogen peroxide solution comprising greater than 65% H₂ O₂by weight.